Floating roof tanks are quite generally employed for the storage of volatile liquids, particularly petroleum products, where it is desired to minimize evaporation losses. In this form of tank, the top closure or roof floats upon the surface of the stored product and rises and falls with the level of liquid within the tank. As the normal position of the floating roof is below the top edges of the tank, it is clear that means must be provided for draining rain water from the surface or deck of the roof to preserve its stability and buoyancy. Accordingly, it is customary to pitch the roof deck toward one or more sumps in which rain water is collected and to provide a conduit connected to the sump and leading downward therefrom through the liquid in the tank, to dispose of the collected water. The drain may be connected to an outlet in the tank wall or bottom so as to dispose of the water.